Stainless Steel 'corrosion'?

[rogerthebodger]

Could very well be exactly the same cause. Wire and tube are manufactured using very similar processes. With wire it seems that these small defects may be due to poor lubrication during the drawing process.

Sorry Vyv the thin wall tube these days are formed by rolling flat sheet into a tube then welding the joint.

Think wall tube used to be made by drawing but most of the thickwall schedule tube I have seem is also rolled and welded.

The flat sheet would be cold rolled not cold drawn.

Wire is of course cold drawn and as such has a very different surface structure and finish,

his is from my days working for Tube investments in the mid 1970's.

 

[Kukri]

Sorry Vyv the thin wall tube these days are formed by rolling flat sheet into a tube then welding the joint.

Think wall tube used to be made by drawing but most of the thickwall schedule tube I have seem is also rolled and welded.

The flat sheet would be cold rolled not cold drawn.

Wire is of course cold drawn and as such has a very different surface structure and finish,

his is from my days working for Tube investments in the mid 1970's.

Thanks.

On behalf of the non-specialists, could you pen a couple of paragraphs on the relevant tube schedules and what they mean?

 

[Kukri]

Minn,

Bit of thread drift here:

You said:

True. And as I think Vyv Cox has pointed out, this is simply because a higher tensile steel is used, possibly because mild steels are not as readily obtainable as higher tensiles in China.

But the trend is true in America, Europe and Australia - all make chain far stronger than specification - whether it is G30 which is almost and sometimes better than G40; G40 or G43 which is near or exceeds G50 strength.

Some G30 chain could be sold as G40, it would meet specification - just (and evidence seems to suggest this is happening). People buy G40 - yet G30 is near G40 quality and has zero failures.

If the welcome and outstanding safety record of G30 over the recent past is as a result of G30 that we all use being 25% overs strength will we enjoy that same safety record if for some reason supply of 'real' G30 is re-established and strength (and yield) drops by 25%.

Jonathan

Two points - as we drift further away - firstly, it is rather likely that the steel used to make the chain will all have come from the same place - China, which really dominates the world steels trade these days, and secondly the attraction of mild steel as opposed to higher tensiles in a marine environment is that it is less prone to sudden failure. Many years ago I approached a very well known shipyard with an enquiry for a large bulk carrier and when they saw our outline specification, with much use of mild steel in the areas most prone to cyclical stresses, they said that "we wanted to build a ship 8,000 tons heavier than she needed to be". Several ships from that yard have since been lost due to sudden and catastrophic hull failures.

Now let's wander gently back to our muttons...

Andrew

 

[Neeves]

Minn (or Andrew), why is high tensile steel more prone to sudden failure than mild steel?

Jonathan

 

[Kukri]

Minn (or Andrew), why is high tensile steel more prone to sudden failure than mild steel?

Jonathan

You would need to ask a metallurgist, preferably one who works for a Classification Society.

 

[rogerthebodger]

Thanks.

On behalf of the non-specialists, could you pen a couple of paragraphs on the relevant tube schedules and what they mean?

Schedule tube or often called gas tube has different wall thickness with the same O/D but specified by nominal bore size (just to confuse matters).

This chart shows the different schedules and wall thichness.

Further info

http://www.shreetube.com/application.html

 

[vyv_cox]

Minn (or Andrew), why is high tensile steel more prone to sudden failure than mild steel?

Jonathan

I don't believe it is but wait to be informed. The point with chain steel is that g40 is a structural type of steel whereas g30 is mild. There is clearly a lot of the former in China but perhaps availability of the latter is very low. G70 is heat treated g40 and widely used in lifting and hoisting where sudden failure would not be tolerated.

 

[rogerthebodger]

Minn (or Andrew), why is high tensile steel more prone to sudden failure than mild steel?

Jonathan

Because it is generally more brittle than lower strength materials

 

[vyv_cox]

Sorry Vyv the thin wall tube these days are formed by rolling flat sheet into a tube then welding the joint.

Think wall tube used to be made by drawing but most of the thickwall schedule tube I have seem is also rolled and welded.

The flat sheet would be cold rolled not cold drawn.

Wire is of course cold drawn and as such has a very different surface structure and finish,

his is from my days working for Tube investments in the mid 1970's.

The tube i weld for pushpits etc. is definitely not ERW. Looks drawn or extruded to me.

 

[rogerthebodger]

I don't believe it is but wait to be informed. The point with chain steel is that g40 is a structural type of steel whereas g30 is mild. There is clearly a lot of the former in China but perhaps availability of the latter is very low. G70 is heat treated g40 and widely used in lifting and hoisting where sudden failure would not be tolerated.

Also in lifting equipment you get shock loading that you can get when lifting. the more brittle nature of higher strength materials could cause sudden failure.

 

[Neeves]

I'm waiting patiently.

I accept that there might be a lot of G40 available in China and less of the G30 - but don't quite understand why American chain shows the same trend. I'm also not sure what 'failure' it has to do with chain as there are simply no reports of failure of the "high tensile" G40 quality chain anyway.

But the idea that high tensile steel is brittle is the old potato being tossed around again. First we'ed need a definition of 'High Tensile' steel but I really don't think any of it is used in the building of commercial ships - the ships would be rather expensive.

 

[Neeves]

Also in lifting equipment you get shock loading that you can get when lifting. the more brittle nature of higher strength materials could cause sudden failure.

Roger

The NACM specification for HT chain demands an extension to break of 20% minimum, for G70 and lower grades the extension to break is 15% min. Higher tensile chain G80, G100 and G120, if made to American specifications, is less brittle than G30.

 

[rogerthebodger]

The tube i weld for pushpits etc. is definitely not ERW. Looks drawn or extruded to me.

That really surprised me. what thickness tube do you use for your pushpit. I use 1.5/1.6 thick 38mm O/D.

ERW is the old way of welding. In my day we were changing from ERW to induction welding of the join.

Due to the polishing the outside welding may not be seen. Have a look inside and if welded there will be a slight ridge and tool marks where the inside weld ridge has been trimmed by a cutting tool.

Can you post a pic of the end of the tube you use looking up the inside.

 

[vyv_cox]

Also in lifting equipment you get shock loading that you can get when lifting. the more brittle nature of higher strength materials could cause sudden failure.

Not with these steels
The carbon content is less than 0.22% - never going to be brittle.

 

[rogerthebodger]

Roger

The NACM specification for HT chain demands an extension to break of 20% minimum, for G70 and lower grades the extension to break is 15% min. Higher tensile chain G80, G100 and G120, if made to American specifications, is less brittle than G30.

This extension that you specify is that under normal tensile testing or is this drop load testing.

The two are quite different types of loading.

 

[Kukri]

I'm waiting patiently.

I accept that there might be a lot of G40 available in China and less of the G30 - but don't quite understand why American chain shows the same trend. I'm also not sure what 'failure' it has to do with chain as there are simply no reports of failure of the "high tensile" G40 quality chain anyway.

But the idea that high tensile steel is brittle is the old potato being tossed around again. First we'ed need a definition of 'High Tensile' steel but I really don't think any of it is used in the building of commercial ships - the ships would be rather expensive.

I'll just leave that here.

I'm suggesting that American chain may be formed from Chinese wire coils.

I respectfully suggest that your knowledge and experience of commercial shipbuilding may be limited.

 

[alant]

The oil & gas industry would not use 316 type stainless steels of any type in a seawater application and instead use the much more highly alloyed super duplex stainless steel or 6Mo austenitic stainless steels. The point that many people forget is that in this type of situation we are not looking at standard seawater at a temperature of around 15deg C. Evaporation of the water will mean that the solids content can increase significantly and heating by the sun can raise the temperature significantly. Hence the advice to rinse a yacht's stainless steel hardware on a regular basis with fresh water or British rain.

Are you suggesting, that these heavy tea stains will wash off in the rain?

 

[Kukri]

Schedule tube or often called gas tube has different wall thickness with the same O/D but specified by nominal bore size (just to confuse matters).

This chart shows the different schedules and wall thichness.

Further info

http://www.shreetube.com/application.html

Thanks, Roger. It's interesting that one cannot easily tell whether pipe is originally welded or not - it was once common practice in haggling over ship specifications with builders to cross out "schedule 40" and write in "schedule 80 seamless" for deck and engine room pipework (not stainless of course) because welded pipe tended to "go" at the weld, given enough years, but it seems we may have all been wasting our time!

 

[Neeves]

Andrew and Roger,

All lifting operators know that you should not snatch load lifting equipment. However I'm ready to be told its quite normal and there is a test for same.

Andrew you made this sweeping statement, in terns of a post on use of steel in chain.

Quote:

"Two points - as we drift further away - firstly, it is rather likely that the steel used to make the chain will all have come from the same place - China, which really dominates the world steels trade these days, and secondly the attraction of mild steel as opposed to higher tensiles in a marine environment is that it is less prone to sudden failure. "

Unquote

There are brittle Grades of High Tensile steel _ Bisalloy make a Q&T steel with a yield of 1500 MPa and tensile strength of 2050Mpa and a rather low elongation at break of 8%. This is an armour plating grade, used in military vehicles, submarines and frigates.

Closer to home they make a range of structural steels, of which our much loved Bis80 is about mid range it has a yield of 630 MPa min, tensile strength of 790 MPa min and an elongation at break of 28%.

Blue Scope our local steel maker make a structural steel with a yield of 300 MPa min and Tensile strength of 400 MPa min and an elongation of 18%

Why would Bis 80 be subject to a more sudden failure than the Blue Scope product? and why is Bis 80 more prone to failure in the marine environment than the Blue Scope product.

I do confess I know nothing whatsoever about commercial ship building and am not entirely sure what connection it has to leisure anchor chains. Its an interesting picture and if the failure has been caused by brittleness of the steel I might hazard to say it was the wrong quality for application or insufficient checks were made as to specification.

But to suggest HT steels are brittle is too all embracing and really needs to be qualified. Furthermore some explanation needs to be provided as to why HT steels are more brittle in the marine environment - particularly as most of us now own anchors with HT steel shanks.

Jonathan

 

[rogerthebodger]

Thanks, Roger. It's interesting that one cannot easily tell whether pipe is originally welded or not - it was once common practice in haggling over ship specifications with builders to cross out "schedule 40" and write in "schedule 80 seamless" for deck and engine room pipework (not stainless of course) because welded pipe tended to "go" at the weld, given enough years, but it seems we may have all been wasting our time!

to determine if the tube is welded or not it is easy with non polished tube but once polished the tel tail signs on the outside is removed. The trimming marks on the inside normally can be seen but I had a look at a some welded tube I had in my workshop and even the inside trimming marks needed careful and detailing inspections to see the marks.

An interesting point all square tube is made round then rolled square/rectangular after welding. I have never seen square solid drawn tube and don't know if its possible.

In my day all thick wall tube (schedule tube) was solid drawn and the thin wall tube welded. As technology moves forward it seems that some thick wall tube id now welded but this must depend on the wall thickness that is required.

As a designer I would alway look of the requirements in terms of strength and ware/corrosion life to determine what type.schedule of tube is required.

Also as a designer I would have no problem in increasing the specification as the only negative effect would be cost as as long as the customer accepts the cost all is OK

This only becomes a contentious issue if the change is made after the contract is agreed and then we get into extra price negotiations.